In a long period , economists were concentrating on the agricultural economic growths . in the history , there were many agricultural economic growths theories and they are possible elucidative to our agricultural economic growths 一直以来，经济学家们都很关心农业经济的增长，不同历史时期，经济学家们对农业经济增长的原因作出了不同的解释。
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During the analysis of innovative leapfrogging , based on the description and remark on the leapfrogging model of brezs , e . - krugman . p . - - tsiddon , d . , the paper puts forward one expanded model , which makes the exogenous technology in the b - k - t model endogenous and shows the function principle and the possibility of backward countries leapfrogging by achieving new technology through input of their own research and development . thereby the model is more comprehensive and more elucidative 论文对每一种蛙跳型式的动力及其运行机理进行了阐释，如对创新型的蛙跳模型进行评述的基础上，提出了一个扩张型模型，把b ? k ? t模型中的外生技术进行了内生化，揭示了后发国通过自身r & d投入获取新技术的条件下蛙跳的可能性及机理，从而使模型更具包容性和现实解释力。
